Many industries, including the assembly processing, grocery and food processing industries, utilize an identification system in which the products are marked with a bar code symbol consisting of a series of lines and spaces of varying widths. A number of different bar code readers and laser scanning systems have been developed to decode the symbol pattern to a multiple digit representation for inventory, production tracking, and for check out or sales purposes. Optical scanners are available in a variety of configurations, some of which are built into a fixed scanning station and others of which are portable. The portability of an optical scanning head provides a number of advantages, including the ability to inventory products on shelves and to track portable items such as files or small equipment. A number of these portable scanning heads incorporate laser diodes which permit the user to scan the bar code symbols at variable distances from the surface on which the bar code is imprinted. A disadvantage of laser scanners is that they are expensive to manufacture.
Another type of bar code scanner which can be incorporated into a portable system uses light emitting diodes (LED) as a light source and charge couple devices (CCD) as detectors. This class of bar code scanners is generally known as "CCD scanners". While CCD scanners have the advantage of being less expensive to manufacture, they limit the user to scanning the bar code by either contacting the surface on which the bar code is imprinted or maintaining a distance of no more than one and one-half inches away from the bar code, which creates a further limitation in that it cannot read a bar code any longer than the window or housing width of the scanning head. Thus, the CCD scanner does not provide the comfort or versatility of the laser scanner which permits variable distance scanning of bar code symbols which may be wider than the window or housing width.
Recently, considerable attention has been directed toward two-dimensional bar codes, which can store about 100 times more information in the same space occupied by a one-dimensional bar code. In two-dimensional bar coding, rows of lines and spaces are stacked upon each other. The codes are read by scanning a laser across each row in succession in a zig-zag pattern. This scanning technique introduces the risk of loss of vertical synchrony. It also has the disadvantage of requiring a laser for illumination of the bar code, which makes the scanner more expensive.